Complexation of zinc(II) and other divalent metal ions by the fluorophore 2-methyl-8-(toluene-p-sulfonamido)-6-quinolyloxyacetic acid in 50% aqueous ethanol

Abstract

A potentiometric and fluorescence study of the complexation of divalent metal ions (M2+) by the fluorophore 2-methyl-8-(toluene-p-sulfonamido)-6-quinolyloxyacetic acid (H2L) in 50% (v/v) aqueous ethanol at 298.2 K and I = 0.10 mol dm–3 (NaClO4) showed that the [ML] and [ML2]2– complexes are characterised by log(β1/dm3 mol–1) and log(β2/dm6 mol–2) values of 8.12 ± 0.20 and 17.06 ± 0.11, respectively, when M2+ = Co2+ and corresponding values of < 8 and 15.73 ± 0.03 when M2+ = Ni2+, 11.96 ± 0.02 and 21.40 ± 0.03 when M2+ = Cu2+, 9.65 ± 0.02 and 19.11 ± 0.06 when M2+ = Zn2+ and 8.44 ± 0.50 and 15.38 ± 0.40 when M2+ = Cd2+. In the cobalt(II) system, [CoL3]4–, where log(β3/dm9 mol–3) = 25.56 ± 0.11, was also detected. The pKa values for H3L+ are 1.87 ± 0.10, 3.72 ± 0.03 and 10.01 ± 0.02. These data are discussed together with the fluorescence characteristics of HL–, [ZnL] and [ZnL2]2–.